Fix #4178: add ability to mass undo tag edits.

Adds checkboxes to the /post_versions index allowing you to select and
undo multiple versions at once.

app/javascript/src/javascripts/post_version.js

@@ -0,0 +1,45 @@
+import Utility from './utility';
+
+let PostVersion = {};
+
+PostVersion.initialize_all = function() {
+  if ($("#c-post-versions #a-index").length) {
+    PostVersion.initialize_undo();
+  }
+};
+
+PostVersion.initialize_undo = function() {
+  /* Expand the clickable area of the checkbox to the entire table cell. */
+  $(".post-version-select-column").on("click.danbooru", function(event) {
+    $(event.target).find(".post-version-select-checkbox:not(:disabled)").prop("checked", (_, checked) => !checked).change();
+  });
+
+  $("#post-version-select-all-checkbox").on("change.danbooru", function(event) {
+    $("td .post-version-select-checkbox:not(:disabled)").prop("checked", $("#post-version-select-all-checkbox").prop("checked")).change();
+  });
+
+  $(".post-version-select-checkbox").on("change.danbooru", function(event) {
+    let checked = $("td .post-version-select-checkbox:checked");
+    $("#subnav-undo-selected-link").text(`Undo selected (${checked.length})`).toggle(checked.length > 0);
+  });
+
+  $("#subnav-undo-selected-link").on("click.danbooru", PostVersion.undo_selected);
+};
+
+PostVersion.undo_selected = async function () {
+  event.preventDefault();
+
+  let updated = 0;
+  let selected_rows = $("td .post-version-select-checkbox:checked").parents("tr");
+
+  for (let row of selected_rows) {
+    let id = $(row).data("post-version-id");
+    await $.ajax(`/post_versions/${id}/undo.json`, { method: "PUT" });
+
+    updated++;
+    Utility.notice(`${updated}/${selected_rows.length} changes undone.`);
+  }
+};
+
+$(document).ready(PostVersion.initialize_all);
+export default PostVersion;

app/javascript/src/styles/specific/post_versions.scss

@@ -0,0 +1,9 @@
+body.c-post-versions.a-index {
+  #subnav-undo-selected-link {
+    display: none;
+  }
+
+  .post-version-select-column {
+    min-width: 2em;
+  }
+}